<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <link rel="stylesheet" href="./css/base.css">
    <style>
        #mainpage{
            position: absolute;
            left: 50%;
            top: 51%;
            transform: translate(-50%,-50%);
        }
    </style>
</head>
<body>
    <div style="width: 100%;height: 50px;background-color: aqua;">

    </div>
    <div id="mainpage">
        <div style="background-color: blue;">
            <input type="text"><button>搜索</button>
        </div>
        
        <div style="background-color: brown; width: 800px;height: 600px;">
            <div>
                
            </div>
        </div>
    </div>
</body>
</html>